(1) Field of the Invention
The present invention relates to a communication terminal and a network unit for use in an information offering system suitably applicable to an ATM network which provides a multicast connection, for example, in an ATM (Asynchronous Transfer Mode), a terminal identifying information setting method, an information offering system, and a fixed-length cell transmitting and receiving unit for use in an information communication system.
(2) Description of the Related Art
FIG. 73 is an illustration of an information offering or distributing system being one example of multimedia services based upon a broadcast mode. In FIG. 73, an information offering system, generally designated at numeral 100, is composed of a service offering unit 101, an ATM network unit 102, and a plurality of (two in this case) leaf node units 103-1, 103-2 serving as service receiving terminals.
In this system, the service offering unit 101 is connected through a service offering channel 104 to the ATM network unit 102 to transmit desired information through the service offering channel 104, thus offering a service of giving multimedia information.
Furthermore, the ATM network unit 102 is for relaying information through the service channel 104 between the aforesaid service offering unit 101 and the respective leaf node units 103-1, 103-2, and not only controls a transmission line between the service offering unit 101 and the leaf node units 103-1, 103-2 but also manages the service offering operation to the leaf node units 103-1, 103-2.
Still further, the leaf node units 103-1, 103-2 function as service receiving terminals which receives, as a service, the information offer from the service offering unit 101 through, for example, the multicast connection.
In more detail, the service offering unit 101 is made up of a service offer processing section 101a, an ATM control section 101b, a transmission line control section 101c, a service control section 101d, and a storage section 101e.
In this arrangement, the service offer processing section 101a is for the purpose of outputting signals constituting various kinds of service offer information (for example, multimedia information such as pictures, voices and data), while the ATM control section 101b conducts the conversion of various kinds of signals from the service offer processing section 101a into ATM cells and the multiprocessing for channels, and further performs the conversion of ATM cells from the transmission line control section 101c into various kinds of signals and the extraction thereof.
Furthermore, the transmission line control section 101c maps the ATM cell from the ATM control section 101b into a transmission signal and further extracts the ATM cell from a transmission signal from the leaf node unit 103-1, 103-2 sides.
Still further, the service control section 101d serves to control the service offering operation to the leaf node units 103-1, 103-2, whereas the storage section 101e acts to register and manage various kinds of information in the service offering unit 101e, and is provided with a service channel corresponding data storage section 101e-1 for registering the aforesaid various information with the service offering channel correspondence and manages them.
Moreover, in more detail, the ATM network unit 102 is provided with two transmission line control sections 102a, 102b, an ATM switch section 102c, an ATM switch control section 102d, a leaf node control processing section 102e, and a storage section 102f.
The transmission line control section 102a conducts the interface processing (for example, the extraction of an ATM cell from a transmission signal, the mapping of an ATM cell into a transmission signal, and others) of a signal between a service offering unit 101 side line or circuit (the service offering channel 104) and the ATM switch section 102c.
In a similar way, the transmission line control section 102b performs the interface processing of a signal between the leaf node unit 103-1, 103-2 side line (the service offering channel 104) and the ATM switch section 102c.
The ATM switch section 102c switches the ATM cell between the aforesaid transmission line control sections 102a, 102b, while the leaf node control processing section 102d manages the leaf node units 103-1, 103-2 on the basis of control information it gets from the leaf node units 103-1, 103-2 through the transmission line control section 102b and the ATM switch section 102c, and further produces control information to be transmitted to the leaf node units 103-1, 103-2.
Furthermore, the ATM switch control section 102d connects the channel for various services from the service offering unit 101 to the leaf node units 103-1, 103-2 in accordance with an instruction the leaf node control processing section 102e gives.
Still further, the storage section 102f serves to register and manage various information in the ATM network unit 102, and includes leaf node control data 102f-1 for registering user control information corresponding to the respective leaf node units 103-1, 103-2 and ATM switch control data 102f-2 for registering control information for conducting processing to establish connection between the service offering channel 104 and the leaf node units 103-1, 103-2.
Moreover, the leaf node control processing section 102e manages user control information, stored with the leaf node control data 102f-1, on the basis of service control information inputted from the leaf node units 103-1, 103-2.
In this system, each of the leaf node units 103-1, 103-2 comprises a transmission line control section 103a, an ATM control section 103b, a service control section 103c, a service instruction section 103d, and a storage device 103e.
The transmission line control section 103a extracts an ATM cell from a transmission signal coming from the ATM network unit 102, and further maps an ATM cell, to be transmitted to the ATM network unit 102 side, into a transmission signal.
Furthermore, the ATM control section 103b converts ATM cells from the transmission line control section 103a into various signals, and further carries out the conversion of various signals, to be transmitted to the ATM network unit 102 side, into ATM cells.
Still further, the service control section 103c recognizes received multimedia information from the ATM control section 103b and offers a multimedia service to the user in accordance with the kind of signal.
Moreover, the service instruction section 103d converts a demand for a multimedia service set by the user as control information into an ATM cell producing demand and outputs the converted demand to the ATM control section 103b. Incidentally, this demand is sent through control channels 106-1, 106-2, provided separately from VPI/VCI of a transmission signal line (the service offering channel 104), to the leaf node control processing section 102e of the ATM network unit 102.
Still further, the storage section 103e registers and manages various information in the leaf node units 103-1, 103-2, and is equipped with a channel data storage section 103e-1 for registering channel information which is in use in the respective leaf node units 103-1, 103-2.
In the information offering system 100 shown in FIG. 73, with this arrangement, a multicast connection is established through the ATM network unit 102 between the service offering unit 101 and the leaf node units 103-1, 103-2, which allows the two leaf node units 103-1, 103-2 to simultaneously receive the same information offered from the service offering unit 101.
With the increase in the number of leaf node units 103-1, 103-2 getting service offers due to the progress of multimedia services such as a digital broadcast using the ATM based upon the broadcast mode, the preparation of a large number of ATM virtual channels (VPI/VCI; Virtual Path Identifier/Virtual Channel Identifier) constituting the service offering channel 104 becomes necessary, which increases the load on the ATM network.
For this reason, in cases where the service offering unit 101 offers the same information to the leaf node units 103-1, 103-2, it is proposed that the information offer is made through the same VPI/VCI between the service offering unit 101 and the leaf node units 103-1, 103-2.
The leaf node unit 103-2 forwards a demand for an information offer through the ATM network unit 102 to the service offering unit 101. If recognizing the fact that the information required by the leaf node unit 103-2 is the same as the information under the offer to the leaf node unit 103-1, the service offering unit 101 issues an instruction for copy of a cell relating to this information toward the ATM switch section 102c of the ATM network unit 102, thus creating the same information to be transmitted through the same ATM virtual channel (VPI/VCI) to the leaf node units 103-1, 103-2.
In the case of the multimedia service such as a digital broadcast based upon the broadcast mode, there is a tendency toward diversification of additional services, and particularly, a requirement has been made for the transmission of information from the service receiving terminal side to the service offering side.
However, since the service offering unit 101 is in connecting relation through the same ATM virtual channel (VPI/VCI) to the leaf node units 103-1, 103-2 receiving the offer of the same information, even if one leaf node receives an ATM cell, difficulty is encountered to identify the leaf node of the sender, and therefore the user management becomes impossible, which makes it difficult to make the aforementioned interactive or two-way communications.
In addition, in the case of transmitting information from the leaf node units 103-1, 103-2 to the service offering unit 101, although it is also possible to employ an ATM virtual channel for point-to-point connections different from the multicast ATM virtual channel (VPI/VCI), with the increase in the number of leaf node units as mentioned before, the enlargement in the ATM virtual channel (VPI/VCI) the ATM network manages occurs so that the load extremely increases.
Even in the case that, for example, different LANs (Local Area Networks) are coupled to each other through an ATM network so that terminals give and receive multimedia information or the like to/from each other between the LANs, it is desirable that the terminals can recognize each other while suppressing the load on the network.